1. Field of the Invention
This invention relates to a motor control system, and more particularly to a motor control system in which a plurality of electric motors can be controlled by a single MPU (microprocessor unit). This invention further relates to an image forming apparatus using such a motor control system.
2. Description of the Related Art
FIG. 7 shows a typical conventional motor control circuit. Motor control circuits using a MPU 50 are broadly divided into a constant-current system motor control circuit and a constant-voltage system motor control circuit. The motor control circuit shown in FIG. 7 is of a constant-current system. In the motor control circuit, pulse motors PM (PM1, PM2 and PM3) are driven under the control of control signals which are respectively input into drivers 51 (driver 1, driver 2 and driver 3) each having a clock terminal CLK (CLK1, CLK2, CLK3) through which a clock for controlling the rotating speed of the motor is input, an enabling terminal ENB (ENB1, ENB2, ENB3) for controlling whether the motor is to be rotated, and a clockwise/counterclockwise terminal CW/CCW (CW/CCW1, CW/CCW2, CW/CCW3).
As shown in FIG. 7, when a plurality of pulse motors PM1 to PM3 are controlled by a single MPU 50, control signals for the respective motors PM1 to PM3 are discretely connected to the MPU 50.
When the MPU 50 has a built-in clock generation means such as an integrated timer controller ITC, pulse motors more than the number of channels which the built-in integrated timer controller ITC can use cannot be controlled unless an additional integrated timer controller 52 is provided. For example, in the example shown in FIG. 7, the third motor PM3 is controlled by the additional integrated timer controller 52.
Such an additional integrated timer controller adds to cost and requires an additional space on the circuit board, which adds to the size of the circuit board.
Generally the MPU 50 is provided with an integrated timer controller ITC having a plurality of channels. When the MPU 50 is incorporated in an apparatus having various mechanisms and processing means (e.g., an image forming apparatus to be described later), all the channels of the integrated timer controller cannot be used for controlling the motors but a part of the channels must be used for controlling other mechanisms and/or the processing means in the apparatus, which gives rise to the aforesaid problem.
For example, in a stencil printer as an example of the image forming apparatus, the number of objects to be controlled by the MPU has been increasing as the number of automated functions of the printer is increased. For example, in the current stencil printer, a large number of motors including those for adjusting the printing position on the printing paper in the longitudinal direction and the transverse direction, for supplying printing papers, and discharging printing papers are incorporated.
Though a plurality of MPU's have been incorporated in the current stencil printer by the function, increasing objects to be controlled has come to require additional integrated timer controllers.